The primate model of hemiparkinsonism produced by the intracarotid infusion of the neurotoxin, 1- methyl -4-phenyl - 1,2,3,6-tetrahydropyridine (MPTP), allows the study of neurochemical changes associated with lesions of the substantia nigra pars compacta. Quantitative autoradiography after in vitro radioligand binding with [3H]naloxone (opiate antagonist) was used to determine the distribution of opiate receptor sites in MPTP-induced hemiparkinsonian moneys. An increased density of opiate sites was observed in the striatum on the side of dopaminergic denervation. The anatomic distribution of these sites resembled the distribution of dopaminergic D, binding sites in the striatum, suggesting potential interactions between dopamine and opioid peptides in the striatum.